SOT capabilities for local helioseismology and expected results

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17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


SOT capabilities for local
helioseismology and expected results

Alexander Kosovichev

Stanford University

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Science objectives for local
helioseismology on Solar
-
B


Quiet Sun


Structure and dynamics of convective cells,
supergranulation and mesogranulation


Dynamics of the high
-
latitude and polar regions


Meridional flow and flux transport (solar
-
cycle dynamo)


Structure and dynamics of supergranulation (properties of
supergranulation waves)


Subsurface structure of small
-
scale magnetic elements


Active Regions


Emerging active regions


Active region evolution in sub
-
surface layers (tracking)


Kinetic and magnetic helicity (local dynamo)


Shearing and twisting flows in active regions, relationship
to flares


17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Unique capabilities of Solar
-
B for
helioseismology


Observations of high
-
latitude and polar
regions (not accessible for MDI hi
-
res FOV).


Tracking of active regions for several days
and monitoring subsurface dynamics.


Observations of wave scattering on magnetic
elements and diagnostics of subsurface
properties of small
-
scale structures.


Helioseismic and photospheric effects of
solar flares.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Time
-
distance measurements

Travel times are determined from
the cross
-
covariance function
(Duvall et al, 1993):

0
(,) (,) (,)
T
f t r f t r dt
 

     

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Deep
-

and surface
-
focusing observing schemes

Surface focusing

Deep focusing

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


SOHO/MDI Helioseismology Data


Full
-
disk Dopplergrams:


2 arcsec/pixel;



2
-
months a year
continuous contact


High
-
resolution
Dopplergrams:


0.6 arcsec/pixel in the
disk center


random 3
-
day campaigns

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


SOT Helioseismology Data

This portion of the
MDI Hi Res Field is
400x400 arcsec.

The rectangle is the
FPP Field, 320 x 160
arcsec. The square
is the central 160 x
160 arcsec.


Time
-
distance

depth range:

0


6 Mm;

temporal
resolution:

2
-
8 hours

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Helioseismology of polar
regions


Solar
-
B has a unique capability to observe
polar regions with high
-
resolution and
measure their structure and dynamics,
providing important data about the
differential rotation and meridional
circulation for dynamo models of the solar
cycle.


Regular synoptic observations of polar
regions are essential.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Internal differential rotation from MDI

The areas of uncertainty are indicated by gray shadow.

The high
-
latitude rotation has not been measured accurately.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Solar
-
cycle variations of
meridional circulation


MDI measurements show that the
meridional circulation below the
surface slows down at the solar
maximum.


Slowing meridional circulation at
the solar maximum creates
difficulties for flux transport
dynamo models to explain
reversals of the polar magnetic
fields.


However, the meridional flows in
high
-
latitude regions have not
been measured.

1996

1997

1998

1999

2000

2001

2002

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Emergence and evolution of active
regions


Solar
-
B will improve the
resolution of sub
-
photospheric structure
of emerging active
regions and associated
flows.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


2001.03.05_20:00 UT, d=2 Mm

Magnetic

field and horizontal flows during


emergence of AR9393

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Sub
-
surface structure and
dynamics of sunspots


Helioseismology
reveals
subsurface
converging flows
below sunspots.
However, the
transition from
the divergent
Evershed and
moat flows on
the surface to
the converging
subsurface flows
is unknown.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Diagnostics of subsurface magnetic fields


2 2 2
2 2 2 2 2 2
( ) 1 ( )
[ ( ) ( ) ]
2
i
c c A
i
c
c c
S S ds
c c c S c k c
  

 

      

A
nU kc
Alfven speed




can

be measured
from the

anizotropy of

travel
-
times.


4
A
c B

 
(Zhao & Kosovichev)

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


High
-
resolution helioseismology
(numerical simulations)


New large
-
scale realistic simulations of solar
convection provide important tests of
helioseismology methods and demonstrate
the potential of high
-
resolution observations
of solar oscillations.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Comparison of the
oscillation power
spectrum and the
time
-
distance
diagrams from MDI
and numerical
simulations.


Analysis of the
realistic
simulations shows
that high
-
resolution
Solar
-
B data will
allow us to improve
the resolution of
helioseismic
images.

Georgobiani et at 2006)
17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Testing time
-
distance measurements
with realistic numerical simulations

Simulation data

Helioseismology

measurement

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Magnetic features:

Top: abs. value of 4
-
hour average mgtm.

Middle: features above some level

Bottom: features not close together


Helioseismology of small
-
scale
magnetic elements

New idea: study the
scattering of waves
on small
-
scale
magnetic elements
(Duvall, 2005)

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Observed and theoretical sensitivity
functions for magnetic elements

Data (Duvall)

Model (Birch & Gizon)

s/Mm^2/kG

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Future Work, Extensions, Ideas


What are we seeing ? B ? down
-
flow ?



Develop a physical model, maybe thin flux
tube: test models of tube oscillations, do
boundary conditions matter ?


Extend modeling to p
-
modes


Joint observations, can see waves coming
up the magnetic element ?


Courtesy of Aaron Birch

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Helioseismology of flaring
regions

-
Where and how does twisting of magnetic
structures occur: in the subsurface layers or in
the dynamo region?

-
What is the role of the local kinetic helicity in
creating the magnetic helicity?


What are the origin and effect of the subsurface
shearing flows?


How deep are the flows that control motions of
the magnetic footpoints in the photosphere?


Are there links between sub
-
photospheric
dynamics and magnetic energy storage and
release in the chromosphere and corona?



17
th

SOT Meeting

NOAJ, April 17
-
20, 2006



There is evidence that kinetic helicity





increases before major flares.

Flares and kinetic helicity

( )
v v dV
 

Helicity density

Zhao, 2004

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Magnetic field dynamics associated
with flares and CME


Magnetic field topology and magnetic stresses in the
solar atmosphere are likely be controlled by motions
of magnetic flux footpoints below the surface
However, the depth of these motions is unknown.


Time
-
distance helioseismology provides maps of
subphotospheric flows and sound
-
speed structures,
which can be compared with photospheric magnetic
fields and X
-
ray data.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Time
-
distance helioseismology analysis

of 2 flares of AR 10486:

1.
X17.2 October 28, 2003, 9:51
-
11:24 UT

2.
X10.0 October 29, 2003, 20:37
-
21:01 UT

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Magnetic field changes in X10 flare,

Oct. 29, 2003, 20:37 UT

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


29
-
10
-
2004, 20:37 UT

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


29
-
10
-
2004, 20:41 UT

Permanent change

Transients

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


20:41 UT

Permanent change

Energy release site

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006



E
II
, erg

Variations of the longitudinal component of magnetic energy

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Two types of magnetic field changes during
the impulsive phase of solar flares:

1.
Permanent changes close the magnetic neutral
line related to magnetic energy release.

2.
Transient variations are caused by high
-
energy
particles.


The permanent changes are consistent with
shrinkage magnetic field lines across the
neutral line (need vector field measurements).


Theoretical paradigm: no magnetic field
changes in the photosphere.

Kosovichev and Zharkova, 1999

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Energy

release site

Sub
-
photospheric flow maps and magnetograms during X10 flare

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


X17.2 flare, Oct. 28, 2003, 9:51 UT

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Energy release site

X17.2 flare, Oct. 28, 2003, 9:51 UT

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Energy

release site

Subsurface shear flows at the energy release site

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


The transient variations caused by high
-
energy particles may generate
“sunquakes”
-

helioseismic response to
solar flares.


Sunquakes are expanding ring
-
like waves
excited by solar flares and observed in the
solar photospere.


17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


First sunquake: July 9, 1996

Kosovichev and Zharkova, 1998

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


These observations suggest that sunquakes are excited by shock waves


propagating downward from the chromosphere into the photosphere,

formed by heating of the chromosphere by high
-
energy electrons



“thick
-
target” model.

Sunquakes correlate with hard X
-
ray flux

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Sunquakes of October 28, 2003, X17 flare

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Time
-
distance propagation diagram of
an October 28, 2003, event

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Sunquake of July 16, 2004, X3.6 flare

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Sunquake of January 15, 2005, X1.2 flare

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Hard X
-
ray sources

Gamma
-
ray sources

X
-
ray,
g
-
牡r⁡湤慣潵獴楣i獯畲捥s潦o報㜠晬慲攬f佣O潢敲o
㈸Ⱐ㈰〳

Doppler sources

> 1 km/s

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Strong (explicitly observed) sunquakes



July 9, 1996, X2.6


October 28, 2003, X17


three events


October 29, 2003, X10


July 16, 2004, X3.6


January 15, 2005, X1.2



No sunquake of comparable magnitude was
observed between 1996 and 2003.


17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Sunspot counts and X
-
flares during
the last three solar cycles.

Graphic courtesy David Hathaway, NASA/NSSTC.

17
th

SOT Meeting

NOAJ, April 17
-
20, 2006


Conclusions


SOT data will provide exciting unique opportunities
for local helioseismology diagnostics of the
subsurface structure and dynamics of the quiet Sun
and active regions.


Coordinated observations with SOHO/MDI and
ground
-
based projects (GONG, South Pole) are
essential.


Substantial work (including large
-
scale MHD
simulations of the solar convection zone) is required
to improve data analysis procedures.